Positive displacement shoe and slat sorter apparatus and method

ABSTRACT

A positive displacement sorter apparatus and method includes providing a plurality of slats being interconnected in an endless web, an upper run of the web defining a conveying surface, and a plurality of pusher shoes gliding along at least some of the slats to laterally displace articles on the conveying surface. A linear motor system is provided to propel the web and includes a plurality of linear motor secondaries at the slats and at least one primary for propelling the secondaries. A control system controls the primaries.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/780,408,filed on Feb. 17, 2004, now U.S. Pat. No. 6,866,136, which is a divisionof application Ser. No. 09/968,742, filed on Sep. 28, 2001, now U.S.Pat. No. 6,814,216, which claims priority from provisional patentapplication Ser. No. 60/236,230, filed on Sep. 28, 2000, and provisionalpatent application Ser. No. 60/278,892, filed on Mar. 26, 2001, thedisclosures of which are hereby incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION

This invention relates generally to conveyor sortation systems and, inparticular, to a positive displacement sorter of the pusher shoe andslat configuration.

Positive displacement sortation conveyors are known having a mainconveying surface and diverter shoes that are generally used to displacearticles laterally on the main conveying surface, such as when thearticles are to be diverted upon one or more spur conveyor linestypically placed at an angle to the main conveying surface. Suchconveyors may include a pair of endless chains and a plurality ofmembers, such as slats, connected at their opposite ends to the chainsin order to provide a moving conveyor surface. Each slat, or every otherslat, is fitted with a pusher or diverter shoe mounted in a manner suchthat the shoe may glide laterally across the slat. Movement of the shoeis guided by a guide track beneath the conveying surface. At the loadingend of the sortation system, the shoes have a particular orientationwith respect to the conveying surface. When an article is to be divertedto a particular spur line, a diverter assembly is actuated to switch aportion of the shoes adjacent the article onto one or more diagonaltracks causing the effected shoes to glide across the slats to divertthe article. Examples of such positive displacement sorters includecommonly assigned U.S. Pat. Nos. 4,738,347 and 5,127,510. Other examplesinclude U.S. Pat. Nos. 3,361,247; 5,409,095; and 4,884,677; and EuropeanPublished Patent Applications EP 0 602 694 B1 and EP 0 444 734 A1.

In many instances, sortation conveyors are driven by rotary motorsoperatively connected to sprockets which propel the chains. As theapplication in which the sortation conveyors are used becomes increasinglarge, the size of the rotary motors must correspondingly increase inorder to provide sufficient power to propel the longer conveyingsurface, as well as achieve the desired throughput. As the size of themotors and sprockets increases in order to meet the additional powerrequirements, the noise issued from the rotary motor, as well as thesizes of the sprockets and chains, correspondingly increase.

There is a long-felt need to increase the throughput of conveyorsystems. Sortation conveyors and their associated induction conveyorsare often the most challenging portion of the conveyor system to handleincreasing demands for article throughput. Increase in throughput can beachieved by increasing the speed of the conveying surface. However,there are difficulties in continuously increasing the speed of theconveying surface. Another way to increase throughput is to decrease thegap between articles while ensuring sufficient gap to allow the articlesto be properly diverted to their destination spur. As gaps get smallerto increase throughput, the necessity to maintain control over the gapsincreases. Because gaps are established by placement of articles on theconveying surface of the sorter and the articles are placed on theconveying surface of the sorter from an induct conveyor, the requirementfor smaller gaps increases the desirability to place and maintain thearticles in proper position on the conveying surface of the sorter.

SUMMARY OF THE INVENTION

The present invention provides a unique positive displacement sorterapparatus and method of controlling same. Aspects of the presentinvention may be utilized with conventional motors, and a unique linearmotor drive system and method of the present invention may be utilizedwith other positive displacement sorter configurations than thosedisclosed herein.

A positive displacement sorter apparatus, according to an aspect of theinvention, includes means for defining a plurality of slats that areinterconnected, thereby defining an endless web. An upper run of the webdefines a conveying surface. The apparatus further including means fordefining a plurality of pusher shoes gliding along at least some of theslats to laterally displace articles on the conveying surface. Theapparatus further includes secondary means for defining a plurality oflinear motor secondaries at the slats, primary means for inducing thrustin the secondaries and thereby propelling the web and control means forcontrolling the primary means.

The apparatus may include a wheel apparatus for supporting the web, thewheel apparatus having wheels at some of the slats rotating about anaxis projecting from an interior of the associated slats. Each of theslats may have an upper surface portion that is substantially planar.Each of the slats may have an outer surface that does not extend abovethe conveying surface for all orientations of the slats. The primary andsecondary means may be either a synchronous linear motor system or anon-synchronous linear motor system. The primary means may be betweenthe upper and lower runs of the web. The secondary means may includemagnet plates in the interior of the slats. The primary means may beadjacent an upper run of the web for propelling slats in the upper runand be positioned where the pusher shoe diverter assemblies are notpositioned. The primary means may be adjacent a lower run of the web forpropelling slats in the lower run from above and produce sufficientthrust to propel the web without elevating the slats in the lower run.

A positive displacement sorter apparatus, according to an aspect of theinvention, includes a plurality of interconnected slats defining anendless web, the upper portion of the web defining a conveying surfaceand pusher shoes gliding along at least some of the plurality of slatsto laterally displace articles on the conveying surface. Each of theslats has an outer surface including upper, lower and side surfaceportions. Either the front or rear surface portion is generally concave.The other of the front or rear surface portions is generally convex. Inthis manner, adjacent slats have cooperatively faced portions. Among themany advantages that may be achieved, this aspect of the inventionprovides for generally uniform gaps between the slats irrespective oforientation of the slats, such as when the slats are traveling betweenupper and lower web portions and the transition portions between theupper and lower web portions.

One of the generally concave and generally convex surface portions mayhave a first enclosing radius of curvature and the other of thegenerally concave and generally convex surface portions may have asecond enclosing radius of curvature with the first and second enclosingradii having a common locus. At least one of the generally concave andgenerally convex surface portions may have a planar segment or may havean arcuate segment. The sorter apparatus may include a wheel apparatusfor supporting the slats. The wheel apparatus may have a slat-supportwheel at a locus of the radius of one of the arcuate portions. The uppersurface portion of the slats may be substantially planar. The outersurface of the slats may be at or below the conveying surface for allorientations of the slats.

A positive displacement sorter apparatus, according to another aspect ofthe invention, includes a plurality of interconnected slats defining anendless web having upper and lower runs and transition portions betweenthe upper and lower runs. The upper run of the web defines a conveyingsurface. Pusher shoes glide along at least some of the plurality ofslats to laterally displace articles on the conveying surface. A linearmotor propulsion system is provided for propelling the web. The linearmotor propulsion system includes at least one motor primary and aplurality of motor secondaries at the slats. The at least one motorprimary is between the upper and lower runs. Among the many advantagesthat may be achieved, the positioning of the at least one motor primarybetween the upper and lower runs reduces the vertical height of thesorter apparatus. This allows the sorter apparatus to be adapted to anincreased number of applications without taking special precautions toaccommodate a higher sorter apparatus.

A positive displacement sorter apparatus, according to another aspect ofthe invention, includes a plurality of interconnected slats defining anendless web having upper and lower runs and transition portions betweenthe upper and lower runs. The upper run of the web defines a conveyingsurface. Each of the slats has a surface configuration. Pusher shoesglide along at least some of the plurality of slats to laterallydisplaced articles on the conveying surface. The sorter apparatusfurther includes a support track network and a wheel apparatus moveablysupporting the endless web for movement on the support track network.The wheel apparatus includes at least one wheel supporting each slat andcouplers for coupling adjacent ones of the slats. A relationship betweenthe at least one wheel and the surface configuration substantiallyavoids a portion of the surface from extending above the conveyingsurface while slats are moving between the upper portion and thetransition portion. Among the many advantages that may be achieved isthe reduction of the likelihood that the outer surface of a slat makinga transition to or from the conveying surface may inadvertently dislodgean article from its location.

The surface configuration may include a front and rear surface portion,one being generally concave and the other being generally convex. Eachmay be generally arcuate having a radius of curvature. The at least onewheel may be at a locus of one of the radii. The upper surface portionmay be substantially planar.

A positive displacement sorter apparatus, according to an aspect of theinvention, includes a plurality of interconnected slats defining anendless web, an upper surface portion of the web defining a conveyingsurface, and pusher shoes gliding along at least some of the pluralityof slats to laterally displace articles on the conveying surface. Alinear motor propulsion system includes at least one motor primaryadjacent the web and a plurality of motor secondaries with the slatsdefining a magnetic interface between the at least one motor primary andany of the motor secondaries passing that motor primary. A lateralstabilizer is provided between each of the pusher shoes in thecorresponding ones of the slats. Among the many advantages that may beachieved, this provides the lateral stabilizer without interfering withthe air gap between the at least one motor primary and the motorsecondaries.

The lateral stabilizer may include a portion of the shoe that islaterally extending and projecting in a recess in the slat, with thelateral stabilizer being substantially outside of the magneticinterface. Each of the slats may have a surface including a lowersurface portion. The lateral stabilizer may be at the lower surfaceportion. The motor secondaries may be adjacent the lower surfaceportion. The lateral stabilizer may be forward of the magnetic interfacewith respect to movement of the web or may be rearward of the magneticinterface with respect to movement of the web. The motor secondaries maybe fixed within the associated slats.

A positive displacement sorter apparatus, according to another aspect ofthe invention, includes a plurality of interconnected slats defining anendless web. An upper portion of the web defines a conveying surface.Pusher shoes glide along at least some of the plurality of slats tolaterally displace articles on the conveying surface. A support tracknetwork is provided, and a wheel apparatus moveably supports the endlessweb for movement on the support network. Each of the slats is made up ofan outer wall having an upper wall portion and a lower wall portion.Each of the slats is mounted to the wheel apparatus with the associatedwheel rotating about an axis projecting to the interior of theassociated slat. Among the many advantages that may be achieved, thiskeeps the mass of the slats close to the support track network, therebyreducing acceleration forces on the web as the web transitions betweenthe upper and lower runs.

The wheel apparatus may further include a plate apparatus couplingadjacent slats. The wheel may be rotatably supported by a shaftconnected with adjacent ones of the plates, thereby pivotally joiningadjacent slats to pivot at the axis mounting the wheel. The mountingmember may be substantially closer to the lower wall portion than to theupper wall portion. Among the many advantages that may be achieved, thisfurther shortens the distance between the bottom of the slat and thetrack apparatus, thereby allowing for a lesser radius at the transitionportions of the web, thereby minimizing vertical height of the sorterapparatus. This is especially advantageous for pusher shoes havingelongated members below each of the pusher shoes because it allows theradius of the transition portion to be reduced without allowinginterference between the elongated members. A plurality of diverterassemblies may be provided for selectively laterally diverting thepusher shoes. The diverter assemblies interact with elongated members.

A positive displacement sorter apparatus, according to another aspect ofthe invention, includes a plurality of interconnected slats defining anendless web having upper and lower portions and transition portionsbetween the upper and lower portions. The upper portion of the webdefines a conveying surface. Pusher shoes glide along at least some ofthe slats to laterally displace articles on the conveying surface. Asupport track network has upper and lower track portions and transitiontrack portions between the upper and lower track portions. A wheelapparatus moveably supports the endless web for movement on the supporttrack network. At least one of the support track network transitiontrack portions has a support surface that is a non-circular curve. Amongthe many advantages that may be achieved, this allows accelerationforces on the slats and shoes to be controlled as the slats and shoesmove through the transition portion having this configuration, therebyallowing the acceleration forces to be controlled in a manner that mayreduce the noise of the web movement.

The support surface may be substantially non-symmetrical about ahorizontal axis. The support surface may have generally larger radii ofcurvature above the horizontal axis than below the horizontal axis, orvice versa. The support surface may be substantially symmetrical about ahorizontal axis. The transition track portion may include a moveableportion to accommodate expansion and contraction of the web. Anexpansion joint may be provided between the moveable portion and theremainder of the support track network to provide track networkcontinuity between the moveable portion and the remainder of the supporttrack. A force-producing member may apply a force on the moveableportion, which may be a substantially constant force irrespective ofposition of the moveable portion.

A positive displacement sorter apparatus, according to another aspect ofthe invention, includes a plurality of interconnected slats defining anendless web having upper and lower portions and transition portionsbetween the upper and lower portions. The upper portion of the webdefines a conveying surface. Pusher shoes glide along at least some ofthe plurality of slats to laterally displace articles on the conveyingsurface. A support track network and a wheel apparatus moveably supportthe endless web for movement on the support track network. The supporttrack network includes a stationary portion, a moveable portion toaccommodate expansion and contraction of the web and an expansion jointbetween the stationary and moveable portions to provide track networkcontinuity between the stationary and moveable portions. Among the manyadvantages that may be achieved, this allows the wheel apparatus tomaintain contact with the support track network.

The expansion joint may include a plurality of interlaced fingers. Aforce-producing member may apply a force on the moving portion. Theforce-producing member may produce a substantially constant forceirrespective of the position of the moveable portion. The moveableportion may be generally horizontally moveable.

A positive displacement sorter apparatus, according to another aspect ofthe invention, includes a plurality of interconnected slats defining anendless web having upper and lower portions and transition portionsbetween the upper and lower portions. The upper portion of the webdefines a conveying surface. Pusher shoes glide along at least some ofthe plurality of slats to laterally displace articles on the conveyingsurface. A support track network and a wheel apparatus moveably supportthe endless web for movement on the support track network. The supporttrack network includes a stationary portion, a moveable portion and aforce-producing member. Movement of the moveable portion with respect tothe stationary portion accommodates expansion and contraction of theweb. The force-producing member applies a substantially constant forceon the moveable portion irrespective of position of the moveableportion. Among the many advantages that may be achieved, this provides amore consistent tension on the web, which, in turn, provides for moreconsistent movement of the web irrespective of the expansion orcontraction of the web.

The force-producing member may apply a substantially horizontal force onthe moveable portion. The force-producing member may include a weightapparatus and a cable system for translating gravitational forceproduced by the weight apparatus to an outwardly directed force on themoveable portion. The weight apparatus may have a mass that isadjustable. The sorter apparatus may include an expansion joint betweenthe moveable portion and the stationary portion.

A positive displacement sorter apparatus, according to another aspect ofthe invention, includes a plurality of interconnected slats defining anendless web having upper and lower portions and transition portionsbetween the upper and lower portions. The upper portion of the webdefines a conveying surface. Pusher shoes glide along at least some ofthe plurality of slats to laterally displace articles on the conveyingsurface. The apparatus includes a support track network and a wheelapparatus moveably supporting the endless web for movement on thesupport track network. A plurality of diverters and associated diverterrails are provided for selectively displacing ones of the pusher shoeslaterally of the conveying surface to displace articles on the conveyingsurface. A frame is provided for supporting the support track network,the diverters and diverter assemblies. The frame includes at least twolongitudinal horizontal members. The horizontal members define fastenerchannels along the horizontal members. The diverters and diverter railscan be selectively mounted at chosen positions along the frame byfasteners engaging the fastener channels. Among the many advantages thatare achieved, this allows the sorter apparatus to be designed fromcommon assemblies irrespective of the application by allowing thelocation of the spurs, and the associated components to be positionedalong the support frame without the necessity for special configurationof the support frame.

The horizontal members may be extruded members. The frame may includesupport legs, which may be selectively mounted at chosen positions alongthe frame by fasteners engaging the fastener channels. The sorterapparatus may include a plurality of cross braces between the horizontalmembers. The cross braces may be mounted at chosen positions along theframe by fasteners engaging the fastener channel. The sorter apparatusmay include a linear motor propulsion system for the web. The linearmotor propulsion system may include at least one motor primary adjacentthe web and a plurality of motor secondaries with the slats. The atleast one motor primary may be selectively mounted at a chosen positionalong the frame by fasteners engaging the fastener channels.

A positive displacement sorter apparatus, according to an aspect of theinvention, includes a plurality of interconnected slats defining anendless web, an upper portion of the web defining a conveying surfaceand pusher shoes gliding along at least some of the plurality of slatsto laterally displace articles on the conveying surface. A closed-looppropulsion system for the endless web is provided. The propulsion systemincludes at least one motor, a web sensor for sensing movement of theweb and a control that is responsive to the web sensor to excite the atleast one motor in a manner that reduces speed fluctuations resultingfrom variations in article loading of the endless web. Among the manyadvantages that are achieved, this allows more accurate positioning ofarticles on the conveying surface from the upstream conveying system,such as an induction conveyor, by ensuring a more accurate speedrelationship between the upstream conveying system and the sorterconveying surface by providing a more closely regulated speed of thesorter conveying surface. This feature is especially beneficial as theloading on the conveying surface varies substantially.

The web sensor may be a slat sensor, such as a proximity sensor, anoptical sensor, an ultrasonic sensor, a microwave sensor, or the like.The web sensor may identify transitions between the slats. The websensor may further identify at least one particular slat. This may beaccomplished by a Hall-effect sensor and at least one magnet in aparticular slat. The web sensor identifies the at least one particularslat by identifying the magnet with the Hall-effect sensor. The websensor may further identify multiple particular slats.

A positive displacement sorter apparatus, according to another aspect ofthe invention, includes a plurality of interconnected slats defining anendless web having upper and lower portions and transition portionsbetween the upper and lower portions. The upper portion of the webdefines a conveying surface. Pusher shoes glide along at least some ofthe plurality of slats to laterally displace articles on the conveyingsurface. A linear motor propulsion system is provided for propelling theweb. The propulsion system includes at least one motor primary adjacentthe web and a plurality of motor secondaries with the slats. The atleast one motor primary propels slats in the lower portion from above.Among the many advantages that are achieved, this allows the linearmotor primary to be positioned in a manner that minimizes verticalheight of the apparatus.

The linear motor propulsion system may be configured to producesufficient thrust to propel the web without substantially elevating theslats in the lower portion. Among the many advantages that are achieved,this allows the linear motor primary to be positioned where desiredwithout resulting in an increase in noise from elevating the slatsagainst gravitation resulting in a noise created by the motion of theweb. A support track network and a wheel apparatus moveably supportingthe endless web for movement on the support track network may beprovided, wherein the support track network supports the lower run frombelow the slats. The apparatus may further include a plurality ofdiverter assemblies to selectively divert the pusher shoes and at leastone other motor primary propelling slat in the upper portion from belowthe slats in the upper portion. The at least one other motor primary maybe positioned where the diverter assemblies are not positioned.

A positive displacement sorter apparatus, according to another aspect ofthe invention, includes a plurality of interconnected slats defining anendless web and an upper run of the web defining a conveying surface.Pusher shoes glide along at least some of the plurality of slats tolaterally displace articles on a conveying surface. A linear motorpropulsion system propels the web. The linear motor system includes atleast a motor primary and a plurality of motor secondaries at the slats.The motor secondaries include magnet plates that are retained in theassociated slats by being fixed from within the associated slats. Amongthe many advantages that are achieved, this facilitates apparatus of thesecondaries to the associated slats and secures positioning of themagnet plates within the slats.

The motor magnet plates may be fixed within the associated slats byinterference fit. The motor magnet plates may be fixed within theassociated slats by deforming portions of the slats. The motor magnetplates may be fixed within the associated slats by dimensionalinterference between the motor magnet plates and the associated slats.The motor magnet plates may be fixed within the associated slats byinserts in the slats, or adhesive, or by welding. The slats may beextruded and may include pockets for the motor magnet plates. Aplurality of motor magnet plates may be provided in each of the slats.This allows the slat to be propelled from linear motor primaries onopposite sides of the web surfaces.

Any of the positive displacement sorter assemblies discussed above mayinclude a linear propulsion system for the web, which may be chosen froma synchronous linear motor system or a non-synchronous linear motorsystem. The propulsion system may include at least one motor primaryadjacent the web and a plurality of motor magnet plates with the slats.The at least one motor primary may be between the upper and lower runsof the web. The motor magnet plates may be in the slats. A plurality ofdiverter assemblies may be provided to selectively laterally divert thepusher shoes. The at least one motor primary may be adjacent an upperrun of the web and adapted to propel slats in the upper run. The atleast one motor primary may be positioned where the diverter assembliesare not positioned. The at least one motor primary may be adjacent thelower run of the web and adapted to propel slats in the lower run fromabove. The at least one primary motor may be configured to producesufficient thrust to propel the web without substantially elevating theslats in the lower run.

A method of sorting articles, according to an aspect of the invention,includes providing a plurality of interconnected slats defining anendless web, an upper portion of the web defining a conveying surfaceand providing pusher shoes gliding along at least some of the pluralityof slats to laterally displace articles on the conveying surface. Themethod further includes providing a web sensor and sensing movement ofthe web with the web sensor and providing a propulsion system comprisingat least one motor. The method further includes exciting the at leastone motor at least as a function of an output of the web sensor therebyreducing speed fluctuations resulting from variations in article loadingof the endless web. Among the many advantages that are achieved, thismethod provides more accurate positioning of articles on the conveyingsurface from the upstream conveying system, such as an inductionconveyor, by assuring a more accurate speed relationship between theupstream conveying system and the sorter-conveying surface.

The web sensor may be a slat sensor, such as a proximity sensor, anoptical sensor, an ultrasonic sensor, a microwave sensor, or the like.The method may further include identifying transitions between slatswith the proximity sensor. The method may further include identifying atleast one particular slat with the web sensor. The web sensor mayinclude a Hall-effect sensor and the at least one particular slat mayinclude a magnet, wherein identifying the at least one particular slatmay include identifying the magnet with the Hall-effect sensor.

The propulsion may be a linear motor propulsion system and the at leastone motor may be at least one linear motor primary and a plurality ofmotor secondaries with the slats. The at least one linear motor primarymay be a plurality of linear motor primaries and the method may furtherinclude exciting the plurality of linear motor primaries as a functionof the output of the web sensor. The exciting of the plurality of linearmotor primaries may include supplying digital signals to the pluralityof linear motor primaries and adjusting the linear motor primaries withthe digital signals.

A method of sorting articles, according to another aspect of theinvention, includes providing a plurality of interconnected slatsdefining an endless web having upper and lower runs and transitions runsbetween the upper and lower runs. The upper run of the web defines aconveying surface. The method further includes providing pusher shoesgliding along at least some of the plurality of slats. The methodfurther includes providing the linear motor propulsion system forpropelling the web. The propulsion system includes at least one motorprimary adjacent the web and a plurality of motor secondaries with theslats. The method further includes propelling slats in the lower runfrom above with the at least one motor primary. The method furtherincludes laterally displacing articles on the conveying surface with thepusher shoes. Among the many advantages that are achieved, this methodallows the linear motor primary to be positioned where desired.

The method may further include producing sufficient thrust to propel theweb without elevating the slats in the lower portion. This reduces noisefrom elevating the slat against gravitation resulting in a noise createdby the motion of the web. Another motor primary may be provided topropel slats in the upper run from below the slats in the upper run.Diverter assemblies may be provided to laterally divert the pushershoes. The at least one other motor primary may be between adjacent onesof the diverter assemblies.

A method of sorting articles, according to another aspect of theinvention, includes providing a plurality of interconnected slatsdefining an endless web having upper and lower runs and transitionportions between said upper and lower runs. The upper run of the webdefining a conveying surface. Pusher shoes are provided gliding along atleast some of the plurality of slats. A linear motor propulsion systemis provided including at least one motor primary and a plurality ofmotor secondaries at the slats. The at least one motor primary ispositioned between the upper and lower runs, and the plurality of motormagnet plates are with the slats. The method further includes laterallydisplacing articles on the conveying surface with the pusher shoes.Among the many advantages that are achieved, this method allows sortingof articles within a vertical space that is small. The magnet plates maybe in the slats.

Any of the above-identified methods may include providing a linear motorpropulsion system that is chosen from one of a synchronous linear motorsystem and a non-synchronous linear motor system. The method may furtherinclude providing the at least one motor primary between upper and lowerruns of the web and may include providing magnet plates in the slats.The method may further include providing a plurality of diverterassemblies and selectively diverting the pusher shoes with the diverterassemblies. The at least one motor primary may be provided adjacent anupper run of the web and propelling slats in the upper run from below.The at least one motor primary may be positioned where the diverterassemblies are not positioned. The at least one motor primary may bepositioned adjacent the lower run of the web and propelling slats in thelower run from above with the at least one motor primary. The at leastone motor primary may provide sufficient thrust to propel the webwithout elevating the slats in the lower run. The method may includepropelling the web at a reduced speed when articles are not beingprovided to the conveying surface. The method may further includeproviding magnet plates in the slats and fixing the magnet plates fromwithin the associated slats. The magnet plates may be fixed within theassociated slats by at least one of interference fit, inserts, adhesiveor welding.

These and other objects, advantages and features of this invention willbecome apparent upon review of the following specification inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a positive displacement shoe and slatsorter assembly, according to the invention;

FIG. 2 is a side elevation of a slat;

FIG. 3 is the same view as FIG. 2 of an alternative embodiment thereof;

FIG. 4 is a top plan view of an endless web;

FIG. 5 is a side elevation of the endless web in FIG. 4;

FIG. 6 a is a side elevation of a transition portion of the endless webin FIG. 4;

FIG. 6 b is the same view as FIG. 6 a with a portion of the wheelassembly removed;

FIG. 7 is an exploded perspective view of an endless web wheel assembly;

FIG. 8 is the same view as FIG. 7 of an alternative embodiment;

FIG. 9 is a combined mechanical and electrical schematic diagramillustrating a sorter assembly propulsion system in side elevation;

FIG. 10 a is a perspective view of a pusher shoe in a slat;

FIG. 10 b is the same view as FIG. 10 a of an alternative embodiment;

FIG. 11 is a side elevation of the shoe and slat combination in FIG. 10;

FIG. 12 is a front elevation of the pusher shoe in FIG. 10;

FIG. 13 is a bottom plan view of the pusher shoe in FIG. 10;

FIG. 14 is a top plan view of the pusher shoe in FIG. 10;

FIG. 15 is a top plan view of a positive displacement shoe and slatsorter system, according to the invention;

FIG. 16 is a flowchart of a control program;

FIG. 17 is a state diagram for the control program in FIG. 16;

FIG. 18 is an electronic schematic diagram of a web sensor;

FIG. 19 is a diagram of a linear motor excitation;

FIGS. 20 a and 20 b are diagrams of linear motor control parameters;

FIG. 21 is the same view as FIG. 2 of an alternative embodiment thereof;

FIG. 22 is the same view as FIG. 2 of an alternative embodiment thereof;

FIG. 23 is the same view as FIG. 2 of an alternative embodiment thereof;

FIG. 24 a is the same view as FIG. 2 of an alternative embodimentthereof;

FIG. 24 b is the same view as FIG. 2 of an alternative embodimentthereof;

FIG. 25 is the same view as FIG. 2 of an alternative embodiment thereof;

FIGS. 26 a and 26 b are the same view as FIG. 2 of alternativeembodiments thereof;

FIG. 27 is an exploded perspective view of a frame assembly;

FIG. 28 is a side elevation of the frame assembly in FIG. 27;

FIG. 29 is an exploded perspective view of a frame end;

FIG. 30 is an exploded perspective view of a take-up assembly;

FIG. 31 is a side elevation of the take-up assembly in FIG. 30;

FIG. 32 is a perspective view of an expansion joint;

FIGS. 33 a–33 d are end elevations of the frame assembly in FIG. 27;

FIG. 34 is a side elevation of a cross support;

FIGS. 35 a and 35 b are alternative embodiments of a frame end;

FIGS. 36 a and 36 b are respective top and bottom plan views of shoetransfer assemblies moving from the top run of the web to a transitionportion and to the bottom run; and

FIG. 37 is a perspective view of a linear motor primary showing acooling system therefor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now specifically to the drawings, and the illustrativeembodiments depicted therein, a sorter assembly 10 is made up of aplurality of slats 20, which are interconnected in an endless web 12with pusher shoes, or diverter shoes, 26 gliding along some or all ofthe slats to laterally displace articles on a conveying surface 11defined by a top run 13 of endless web 12 (FIG. 1). Diverter assemblies16 laterally displace pusher shoes 26 to divert articles onto selectedspurs 17 in order to sort the articles (FIG. 15). To do this, diverterassemblies 16 include diverter rails extending diagonally across theconveying surface beneath the web and diverter switches to divert pushershoes to individual diverter rails. Each of the slats has an outersurface 33, including an upper surface portion 33 a, a lower surfaceportion 33 b, a forward surface portion 33 c and rear surface portion 33d (FIGS. 2 and 3).

Sorter assembly 10 may be of the parallel divert type as disclosed incommonly assigned U.S. Pat. No. 5,165,515; of the diagonal divert typeas disclosed in commonly assigned U.S. Pat. No. 5,127,510; or acombination of the parallel and diagonal divert type as disclosed incommonly assigned U.S. Pat. Nos. 6,041,909 and 5,927,465, which are allhereby incorporated herein by reference.

Upper surface portion 33 a is defined by an upper wall 34. Lower surfaceportion 33 b is defined by a lower wall 36. Forward surface portion 33 cis defined by a front wall 38. Rear surface portion 33 d is defined by arear wall 40. The terms “front” and “rear” are relative terms to assistin understanding the disclosed embodiment and should not be consideredlimiting. Indeed, although endless web 12 may move in the direction offorward surface portion 33 c leading, it is also capable of moving inthe direction of rear surface portion 33 d leading. References to“upper” and “lower,” and the like, with respect to a slat or a pushershoe are relative to the slat or the shoe in the upper run of the web.The terms “longitudinal” or “longitudinally” refer to direction ofmovement of the endless web. The terms “lateral” or “laterally” refer todirection from side-to-side of the conveying surface, or perpendicularto direction of movement. In the illustrative embodiment, upper surfaceportion 33 a is generally planar, meaning that it is sufficiently planarto present a generally continuous conveying surface 11, but may havevarious surface features in the upper surface portion 33 a, such asridges, valleys, and the like.

Forward surface portion 33 c has a generally convex portion 35 a. Rearsurface 33 d has a generally concave portion 35 b. As used herein, theterm “convex” means curved or rounded in cross-section taken through alongitudinally oriented vertical plane, like the exterior of a circle,or the term “convex” may also mean being a continuous function, or partof a continuous function, with the property that a line joining any twopoints on its graph lies on or above the graph. The term “convex” mayalso mean concave inwardly. As used herein, the term “concave” meanshollowed or rounded inward in cross-section taken through alongitudinally oriented vertical plane. The term “concave” may also meanthe side of a curve or surface on which neighboring normals to the curveor surface converge and on which lies the chord joining two neighboringpoints of the curve or surface. The term “concave” may also mean concaveoutwardly. The surface portions 35 a, 35 b of adjacent slats havecommon-faced portions that maintain their common interface throughnormal changes and orientations of the slats as they move about theendless web 12. This assists in maintaining a generally constant gapbetween adjacent slats as the slats move throughout the endless web 12.In the embodiment illustrated in FIGS. 2 and 3, the facing portions 35a, 35 b are generally arcuate. However, they may be made up of a seriesof surface segments, such as planar segments S, that are not arcuate,but form facing convex and concave surfaces, as shown, for example, inFIG. 24 b, or may be a combination of arcuate and planar surfacesegments. Further, as shown in FIGS. 2 and 3, the concave and convexsurfaces may be asymmetrical above and below their respective verticalmidpoints, but may, alternatively, be symmetrical above and below thevertical wide points.

One of the front surface 33 c and the rear surface 33 d forms aprotrusion. The other forms a recess so that the protrusion on one slatis positioned adjacent the recess of the other so that the surfaces havecooperative positioning. One of surfaces 33 c and 33 d may penetrate therecess of the other surface or it may not penetrate the recess of theother surface. In embodiments in which one of the surfaces 33 c and 33 dpenetrates the other surface, a linear vertical passage between adjacentsurfaces 33 c and 33 d is beneficially avoided and, thus, the potentialfor objects becoming lodged between adjacent surfaces 33 c and 33 d isreduced. Convex surface portion 35 a has an enclosing radius R₁, whichshares a common locus L with an enclosing radius R₂ of concave surfaceportion 35 b. The term enclosing radius means the radius of an arcuateportion, such as seen in FIG. 2, or the radius of the closest fittingarcuate portion of the planar sections S, such as seen in FIG. 24 b.Radius R₂ may be greater than or equal to radius R₁.

Slats 20 are maintained in their respective position in endless web 12by a wheel assembly 24 (FIGS. 4–8). Wheel assembly 24 includes at leastone wheel 112, which is rotatably mounted about an axis that passeslaterally to interior 42 of slat 20. This may be accomplished byrotatably mounting wheel 112 at a mounting member, such as circularchannel 52. Circular channel 52 is generally at the loci of radii R₁ forconvex surface portion 35 a of forward surface portion 33 c. This allowsconvex surface portion 35 a to maintain a substantially constant heightwith respect to adjacent slats as the slats move throughout endless web12. More particularly, sortation assembly 10 additionally includes aframe 18 defining a support track network 19, made up of correspondinglateral tracks 19 a, 19 b on opposite lateral sides of frame 18. Withwheel assembly 24 riding on respective support tracks of support tracknetwork 19, each slat pivots about the axis of rotation of wheel 112positioned at mounting member 52. As a result, as slats move toward andaway from top run 13, from and to transition portions 15, there issubstantially no portion of surface 33 which extends above conveyingsurface 11, as can best be seen in FIG. 5. This avoids the misalignmentof articles on conveying surface 11 by protruding portions of a slat asthe slat moves from a transition portion to or from the top run 13.

Wheel assembly 24 additionally includes a plate 88 between adjacentslats 20. Plates 88 are affixed with a fastener 89 engaging anothercircular channel 54 in slat 20 and the shaft-supporting wheel 112. Inaddition, an extension 90 of plate 88 pivotally joins a portion of theadjacent slat, such as the shaft-supporting wheel 112, thereby joiningthe adjacent slat and providing pivotal movement between the slats.Slats 20 are coupled to wheel assembly 24 at each end of the slat. Asshown in FIG. 8, plate 88 has an offset bridge portion 90. Plate 88 isgenerally parallel to bridge portion 90 in separate planes. An end 92 ofplate 88 has a convex front surface 94, which has approximately the sameconfiguration as convex front wall 38 of slat 20. The height of plate88, as defined between bottom edge 96 and top edge 98, is substantiallyequal to the height of slat 20 as defined between lower wall 36 andupper wall 34. Plate 88 includes a pair of through-holes 100, 102,placed in spaced relation, while bridge portion 90 includes an enlargedthrough-hole 104 formed with an annular flange 106.

A collar 108, having a reduced width portion 110, is placed throughthrough-hole 104. Collar 108 is placed in registry with through-hole 102of plate 88 of the immediately preceding bridge portion 90 in thedirection of travel of conveying surface 11. Wheel 112 is attached toreduced width portion 110 of collar 108, and an axle (not shown) isplaced through wheel 112, through-hole 104, collar 108, through-hole 102of plate 88 of the immediately preceding end member 24, and circularchannel 52 of slats 20, and, hence, couples adjacent slats 20 to eachother. Wheel 112 rotates about a substantially horizontal axis lateralof the conveying surface. The purpose of first wheel 112 is to supportweb 12 and allow the web to travel along the support track network.

A generally L-shaped member 114 is formed having an aperture 116 formedin vertical section 119 in registry with through-hole 100 of plate 88and circular channel 54 of slat 20. A horizontal section 118 of L-shapedmember 114 includes a pin 120 projecting from a bottom surface 118′, towhich a second wheel 122 is rotatably attached. A suitable fastener 89is threaded through aperture 116 of L-shaped member 114, through-hole100 of plate 88 and circular channel 54 of slats 20 to provide a secondcoupling site for each end member 24. When assembled, wheel 122 ispositioned below lower wall 36 of slat 20. The purpose of wheel 122 isto maintain the lateral orientation of slats 20 as the same travellongitudinally over the track assembly. Although wheel assembly 24 isillustrated having a second wheel 122 associated with each slat, it willbe recognized that this is not critical, and that a second wheel 122 maybe attached to every other, third, or fourth slat or more withoutdeparting from the spirit and scope of the invention.

In an alternative embodiment, wheel assembly 24′ includes a second wheel122 positioned at a lateral height of plate 88′. Plate 88′ may benotched at K, the interface between adjacent slats, to reduce thelikelihood of a diverted article from contacting plate 88′. Otherwise,wheel assembly 24′ is generally the same as wheel assembly 24.

Each support track 19 a, 19 b includes a fixed portion 21 a, 21 b, and amoveable portion 23 a, 23 b (FIG. 9). An expansion joint 25 accommodatesmovement between moveable member 23 a, 23 b and fixed portion 21 a, 21b. Expansion joint 25 includes a series of interlaced longitudinalfingers that provide a continuous track for wheels 112 notwithstandingthe position of moveable member 23 a, 23 b. A force-producing device 27applies an outward, generally horizontal, force on moveable member 23 a,23 b, thereby maintaining a consistent tension to web 12 irrespective ofexpansion and contraction of the web, such as due to temperaturevariations, and the like. Force-producing device 27 may produce aconsistent force irrespective of the position of moveable member 23 a,23 b, as will be explained in more detail below. Endless web 12 has abottom run 14, which is supported by a bottom portion 22 a, 22 b offixed portion 21 a, 21 b of the support track network. Transitions 29between bottom portions 22 a, 22 b and transition portions 31 a, 31 b ofsupport track 19 a, 19 b allow endless web 12 to move between the innersurface of the bottom portions 22 a, 22 b and the outer surface of theremaining portion of support tracks 19 a, 19 b. This allows endless web12 to be supported from below at both top run 13 and bottom run 14.Transition portion 29 is expandable in unison with movement of moveablemembers 23 a, 23 b, but is not a joint, per se. Transition portions 15of web 12 are tensioned around the transition portions 31 a, 31 b ofsupport tracks 19 a, 19 b.

Pusher shoe, or diverter shoe, 26 is a wraparound shoe (FIGS. 10–14),generally of the type disclosed in commonly assigned U.S. Pat. No.5,127,510, the disclosure of which is hereby incorporated herein byreference. Pusher shoe 26 preferably includes a generally concavetrailing sidewall 81 and a generally convex leading sidewall 83. As withfront surface 33 c and rear surface 33 d of slats 20, convex leadingside wall 83 and concave trailing side wall 81 may be arcuate or may beformed of a series of surface segments, such as planar segments, and maybe asymmetrical relative to respective vertical midpoints or,alternatively, may be symmetrical. Pusher shoe 26 includes inwardlyextending projections 80, 82, which project inward from trailingsidewall 81 and leading sidewall 83, respectively, and act uponrespective channels 44, 46 in the associated slat 20 to provide bearingmeans for resisting rotational forces about the long axis of thecorresponding slat 20 and about an axis parallel to the direction oftravel of the corresponding slat 20, as disclosed in the commonlyassigned '510 patent. An inward projection 84 of pusher shoe 26 glidingin a channel 48 of slat 20 provides a lateral stabilizer to resistrotational motion of shoe 26 about a vertical axis, as disclosed in thecommonly assigned '510 patent. Alternatively, a projection of the slatcould glide in a channel of the shoe to provide a lateral stabilizer.

Shoe 26 may be a one-piece shoe molded from a plastic material, such asnylon, Delrin, acetal copolymer, or other known durable plastic moldablematerial and is made up of a series of wall segments having asubstantially uniform thickness as disclosed in the commonly assigned'510 patent. Although the pusher shoe 26 is illustrated as a one-pieceshoe, it could also be made in separate glide portions and diverterportions, as disclosed in the '510 patent. Pusher shoe 26 may be madefrom a self-lubricating plastic material or may include lubricatingstrips (not shown) between inward projections 80, 82 and/or 84 andrespective channels 44, 46 and 48. The lubricating strips may be stripsthat fit over the respective inward projection or, otherwise, areretained in functional relationship thereto. Pusher shoe 26 includesmeans defining one or more diverting surfaces 37, such as by ahigh-friction insert, or the like, as disclosed in the '510 patent. Inan alternative embodiment, pusher shoe 26 may have the configuration ofthe pusher shoe disclosed in U.S. Pat. No. 5,127,510, but with thelateral stabilizer modified to accommodate positioning of the secondarywithin the slat. Alternatively, pusher shoe 26 may have theconfiguration disclosed in European Patent EP 0 602 694, the disclosureof which is hereby incorporated herein by reference.

In an alternative embodiment, pusher shoe 26′ includes a concavetrailing side wall 81′ and a convex leading side wall 83′ that mayeither or both have non-arcuate planar portions 85 (FIG. 10 b), butwould, otherwise, be generally the same as pusher shoe 26.

Pusher shoe 26 may include a transfer assembly 30 of the type disclosedin commonly assigned patent application Ser. No. 09/840,639, filed Apr.23, 2001, by Veit et al. for a SORTATION SYSTEM DIVERTER SWITCH, thedisclosure of which is hereby incorporated herein by reference,extending downwardly from the pusher shoe. Transfer assembly 30 is anelongated member utilized to divert the pusher shoe to a guide rail andto guide the pusher shoe along a guide rail of a diverter assembly 16 inorder to divert packages. Diverter assembly 16 may be of the typedisclosed in commonly assigned patent application Ser. No. 09/606,610,filed Jun. 29, 2000, by James T. Shearer, Jr. et al., for a CONVEYORSYSTEM WITH DIVERTING TRACK NETWORK, the disclosure of which is herebyincorporated herein by reference. Because transfer assembly 30 iselongated in the direction of movement of endless web 12 and protrudesdownwardly from pusher shoes 26, care must be taken to avoid contactbetween associated transfer assemblies 30 as the corresponding slats 20move at transition portions 15 along transition portions 31 a, 31 b ofsupport track network 19. As would be apparent to those skilled in theart, the reorienting of the slats at transition portions 15 movestransfer assemblies 30 of adjacent pusher shoes 26 closer together. Thisis a function of the distance, or lever arm, between transfer assemblies30 and the pivot of the associated slats 20, which, in the illustratedembodiment, is at mounting member 52. Advantageously, slat 20 hasmounting member 52 positioned closer to lower wall 36 than to upper wall34. Because mounting members position the axis of rotation of wheels112, this reduces the distance between transfer assembly 30, whichextends from a bottom portion of the shoe, and the pivot point for eachslat. This, in turn, reduces the amount of pivotal movement of eachtransfer assembly 30 toward the adjacent transfer assembly 30 for agiven radius of transition portion 31. By providing mounting portion 52closer to lower wall 36 than to upper wall 34, it is possible todecrease the radius of transition portion 15. This decrease in radiusallows the top run of endless web 12 to be closer to the bottom run 14of endless web 12. This, in turn, reduces the overall height of sorterassembly 10. As is understood by those skilled in the art, it may bedesirable to reduce the vertical height of the sortation assembly insome applications. Indeed, sortation assembly 10 may be applied inlocations, which would, otherwise, require trenching the floor at thelocation of the sortation assembly to accommodate a vertically highersorter assembly than that provided herein.

As an enhancement to facilitate a further reduction in sorter assemblyheight, the transfer assemblies 30 could be oriented on a diagonal priorto entering a transition portion of the web 15 from top run 13 (FIG. 36a). This allows the radius of the rails to be further reduced withoutinterference between adjacent transfer assemblies. This may beaccomplished by an orienting device 300, such as by a magnet that issuitably positioned to attract a portion of the transfer assembly.Transfer assemblies 30 can be reoriented in a linear aligned fashioncoming out of the transition portion 15 to bottom run 14 by areorientation device 302. A similar orientation and reorientation of thetransfer assemblies can occur between bottom run 14, transition portion15 and top run 13.

Sorter assembly 10 has a propulsion system 41, which, in theillustrative embodiment, is a linear motor propulsion system. Linearmotor propulsion system 41 includes one or more linear motor primaries28 and a plurality of linear motor secondaries 63 at the slats. At theslat means, the adjacent or part of wall 34, 36, 38, 40 is either insideor outside of the slat. In one embodiment, linear motor secondariesinclude magnet plates 64 within interior 42 of some or all of the slats20 in combination with lower wall 36 of the slat (FIG. 2). Magnet plates64 are positioned in a portion of interior 42 closest to primary 28.Primary 28 is closely spaced from slat 20 defining a slat gap SG betweena face of primary 28 and a corresponding face of slat 20 and a magneticgap MG between a face of primary 28 and magnet plate 64 (FIG. 3). As asecondary 63 passes a primary 28, a magnetic interface MI exists at theprojection of magnet plate 64 on primary 28, or vice versa. In order tominimize magnetic gap MG, lateral stabilizers made up of inwardprojection 84 and channel 48 may be outside of magnetic interface MI. Inthe embodiment illustrated in FIG. 2, the lateral stabilizer is adjacentrear wall 40. In an alternative embodiment illustrated in FIG. 3, slat20 a has a lateral stabilizer that is adjacent front wall 38. Otherpositions may suggest themselves to the skilled artisan. In anotheralternative embodiment illustrated in FIG. 26 a, a pusher shoe and slat,each of conventional configurations, are further provided with a magnetplate 64 a in the slat. The lateral stabilizer could be positionedbetween the front and back of the shoe with the linear motor magnetplate 64 forward or rearward of the lateral stabilizer, as illustratedin FIG. 26 a. The lateral stabilizer could also be put on upper wall 34.Indeed, magnet plate 64 could be divided into two magnet plates with thelateral stabilizer between the two magnet plates. Alternatively, theshoe and slat disclosed in U.S. Pat. No. 5,127,510 may be provided witha magnet plate located within the base of the outwardly projectingprotrusion of the slat, which makes up part of the lateral stabilizer.In such an alternative, the front-to-back dimension of the base 304 ofthe lateral stabilizer protrusion may be increased to accommodate thesecondary 64, as shown in FIG. 26 b. Preferably, the lateral stabilizerwould be substantially outside of the magnetic interface MI.

Magnet plate 64 is positioned in a receiving section 62 of slat 20.Magnet plate 64 is fixed from within the corresponding slat. This avoidsthe need for fasteners, which must be separately applied through theslat into engagement with an opening in the magnet plate after themagnet plate has been positioned therein. One way to fix the magnetplate from within the slate is to provide receiving section 62 with oneor more detents, illustrated as 65 and 66, which fix magnet plate 64from within the slat. The relative dimensions of magnet plate 64 andslat 20 provide an interference fit between magnet plate 64 and detents65 and 66. However, other techniques may be used to fix magnet plate 64from within slat 20, such as by deforming a portion of a wall 34, 36, 38or 40 toward the magnet plate, as illustrated in FIG. 25, or by usinginserts, such as plastic inserts, or the like, in order to interlock thesecondary with the slat. This is especially useful to accommodatevariations in dimensions of the slat and may be deformable to match theparticular slat and magnet plate interface. Alternatively, magnet plate64 may be adhered in place, such as by welding, adhesive, or the like.

Linear motor primaries 28 may be, advantageously, positioned withinendless web 12 (FIG. 9). Linear motor primaries 28 may be adjacent toprun 13 of the endless web and drive slats 20 from beneath. Primaries 28may be above bottom run 14 and drive slats 20 from above. Separateprimaries 28 may be adjacent both top run 13 and bottom run 14. Linearmotor primaries 28 adjacent top run 13 may be positioned where thediverter assemblies 16 are not positioned, such as between diverterassemblies 16 (FIG. 15). This allows the linear motor primaries to beimmediately adjacent endless web 12 without interfering with thediverting of pusher shoes 26. While the primaries 28 are shown on thelateral centerline of the web, it should be understood that they may beoffset from the lateral centerline and may be staggered. Also, more thanone primary may be provided side-by-side, such as to drive move than onesecondary for each slat.

Support track network 19 supports bottom run 14 from below. Therefore,the weight of the bottom run 14 holds the bottom run against the supporttrack network. Linear motor primaries 28 driving slats in bottom run 14provide a thrust, or propulsion, force FT tending to propel web 12 andattraction force FA tending to attract the motor magnet plates, and,hence, the slats toward the linear motor primaries. Secondaries 63 aredesigned in a manner, and linear motor primaries 28 adjacent bottom run14 are controlled in a manner, to limit force FA to a level that willnot substantially elevate bottom run 14 off support track network 19.This substantially reduces any noise from slats 20 being raised by forceFA and then dropped against support track network 19 when the slat movesbeyond the primary.

Sortation assembly 10 includes a propulsion control system 500.Propulsion control system 500 in combination with propulsion system 41provides a closed-loop propulsion system for endless web 12. Propulsioncontrol system 500 includes a web sensor 502, which supplies an output503 to a linear motor controller 504. Propulsion control system 500additionally includes linear motor drives 506, each of which supplies ahigh current at an output 508, which supplies current to the respectivelinear motor primary 28. Linear motor drives 506 are conventional motorcontrollers, such as variable frequency drives, which are capable ofenergizing the respective linear motor primary 28. Such linear motordrives are commercially available from various sources, such as SiemensA. G., Mitsubishi, Ltd., and the like. Each linear motor drive receivesan input 510, which establishes the output of linear motor drive 506 andthereby the nature of the excitation current applied to the linear motorprimary at output 508. Conventionally, input 510 is a variable signal,such as an analog voltage, that may vary from between 0 and 5 volts orbetween 0 and 10 volts, or the like. The magnitude of the analog voltagecontrols the frequency of the output of linear motor drive 506 such thatthe greater the magnitude of the input voltage at 510, the higher thefrequency of the output at 508 of the corresponding linear motor drive506. Input 510 is established by an addressable interface 512.Interfaces 512 are individually addressable by linear motor controller504 over a digital interface 514. Digital interface 514 allows linearmotor controller 504 to individually address each interface 512 in orderto set the input 510 for the associated linear motor drive. Digitalinterface 514 may be a conventional bus, such as a CAN, LAN, Ethernet,or other known conventional or custom bus system.

Web sensor 502 senses the passing of each slat 20 and thereby providesinformation over output 503 to linear motor controller 504 relevant tothe speed of web 12. In order to accomplish this sensing, web sensor 502may be a proximity sensor, such as an inductive proximity sensor, anoptical sensor, an ultrasonic sensor, a microwave sensor, or the like.Web sensor 502 senses the gap, or transition, between slats, but may,otherwise, sense the movement of the slats, such as by direct contactwith the slats, or the like. Web sensor 502 may also have the capabilityof identifying individual slats. For example, web sensor 502 may includea magnetic sensor, such as a Hall-effect sensor 572, which senses one ormore magnets in one or more slats 20. This provides a confirmation tocontroller 504 that the slat speed sensor 560 is operating properly byhaving a confirmation that the slat that should be passing over at aparticular time, such as a slat designated the lead slat, corresponds tothat determined by the integration of the speed of web 12.

Linear motor controller 504 sends out digital signals on digitalinterface 514 to each addressable interface 512 in order to establishthe output thereof and thereby the speed of the corresponding linearmotor drive. This arrangement allows the ability of linear motorcontroller 504 to control the output of linear motor drive 506. Incertain applications, sortation assembly 10 may be at a great length,measuring hundreds of feet, creating an advantage of utilizing a linearmotor propulsion system. This conversion of the digital command to ananalog signal at each linear motor controller, reduces the necessity forconventional conditioning of the analog input to the linear motor drives506 that are spaced distantly from linear motor controller 504.Moreover, propulsion control system 500 allows each linear motor drive506 to be individually controlled. For example, under acceleration orheavy load conditions, linear motor controller 504 may energize all ormost linear motor drives 506 in order to provide sufficient propulsionto web 12. Under other conditions, such as lightly loaded conditions orduring steady-state operation, linear motor controller 504 may cause oneor more addressable interfaces 512 to instruct the associated linearmotor drive 506 to supply an output 508 to the associated linear motorprimary 28 corresponding to a reduced, or no, thrust. Other examples ofthe use of propulsion control system 500 to individually control linearmotor drives 506 would suggest themselves to the skilled artisan and areall intended to be covered herein.

Propulsion control system 500 includes a control program 520 (FIG. 16).Control program 520, in the illustrated embodiment, is carried out bylinear motor controller 504 which is microcomputer-based. Controlprogram 520 begins at 522 and initializes at 524 a control loop filter.The control loop filter, which includes speed filters, and the like, isprovided in order to limit response to rapid fluctuations in the outputof web sensor 502. The control then calculates at 526 the speed of bed12, such as by reading outputs 503, and applies a window filter to thespeed inputs at 528. The window filter is in order to keep the PIDportion of the control loop from reacting inappropriately to suddenchanges in web speed reported by the web sensor. For example, the windowfilter reduces the tendency of the PID portion of the control fromover-responding to changes in web speed. This may be accomplished byaveraging a certain number of the previous values in a window in orderto filter the commands.

It is determined at 530 whether a filter auto-sizing is enabled. If so,the filter is resized at 532. The filter is sized to give responsivenessto the loop. If the sample rate changes, such as a result of systemloading, the sample rate will be changed to maintain the time constantof the filter. The filter may be resized to keep the delays in theclosed-loop control at a minimum and predictable. This is because areduction in the responsiveness of the speed control reduces the abilityof the control to keep the speed of the web within a narrow tolerance. Abed speed error is calculated at 533 and a plant command is thencalculated at 534. The plant command is the voltage that is to beproduced at 510 to select a particular output of linear motor drive 506in order to effect the change in the thrust that is desired. This mayalso include a scaling factor, if required, in order to adapt to theparticular parameters of the linear motor drive 506 being utilized.Controller 504 then sends a command at 536 over digital interface 514 toindividual addressable interfaces 512.

Control program 520 determines at 538 how fast the loop is processing inorder to ensure that the loop is progressing properly and repeatably. Ifa speed control loop is being delayed and/or slowed, control program 520could notify an upper level of control (not shown). Control 520 thendetermines whether a state machine 540 needs to be updated at 542. It isthen determined at 544 whether a logging function is enabled. If thelogging function is enabled, data, such as bed speed, bed speed error,plant command in hertz, or the like, is logged at 546. This loggingfunction allows the system to monitor how the sorter responds to change,such as in loading or in speed variation. It also allows the control toaccumulate historical data to detect errors in portions of the sorterassemblies, such as wheel bearings producing excessive drag, or thelike. The control then determines at 548 whether the execution of thecontrol loop falls outside of control loop parameters. If so, theoutputs of the addressable interface 512 are set to a “safe” state at550 combined with a notification to an operator of a failure condition.The “safe” state may be a zero speed condition or it may be a reducedspeed condition. If it is determined at 558 that the execution is notoutside of the control loop, control returns to 226 where the slatsensor is, again, accessed and the control loop executes once more.

State machine 540 determines the state of the control loop andestablishes parameter limits of closed-loop control depending upon itsstate (FIG. 17). State machine 540 includes a stopped state 552, a bedacceleration state 554 during which the linear motor propulsion systemis accelerating the bed, an idling state 556 during which no adjustmentis being made to the speed of the bed, and a deceleration state 558during which the linear motor propulsion control is decelerating thebed. For each state 552–558, a determination is made whether the speederror is within an acceptable range and, if not, the control moves to adifferent state in order to effect the appropriate function.

Web sensor 502 includes a proximity sensor 560 in the form of a tuned LCcircuit, which is supplied with an oscillating square wave by anoscillator 562 at an oscillator line 564 (FIG. 18). Oscillator line 564is connected with an external input 503, should it be desired to supplythe oscillating signal from an external source, such as controller 504.If so, the components making up oscillator 562 would be excluded fromthe circuit. Oscillator line 564 is supplied to proximity sensor 560 andto an EXCLUSIVE OR circuit 566. The output of proximity sensor 560 issupplied through an amplifier 568 to the other input of EXCLUSIVE ORcircuit 566 whose output is integrated by an integrator 568. The outputof integrator 568 is supplied at 570 as a slat detection signal.Proximity sensor 560 operates by changing its resonant frequency in thepresence or absence of the metal surface of each slat, which causes aphase shift between the inputs to EXCLUSIVE OR 566. The phase shiftresults in a variation in the output, which is integrated by integrator568, and thereby output 503 varies with the presence or absence of thegap between slats.

Web sensor 502 may additionally include a particular web identifier inthe form of a magnetic sensor 572. Magnetic sensor 572 may be aHall-effect sensor or other type of sensor, such as a reed switch, orthe like, that senses a magnetic field. Magnetic sensor 572 detects oneor more permanent magnets, either the North Pole, South Pole, or bothNorth and South Poles. Such magnet, or magnets, may be positioned in oneslat, designated an index slat or in more than one slat, in which casethe magnets may be arranged in a unique arrangement in each of the slatsin a coded fashion. The output of magnetic sensor 572 is supplied as anoutput at 503. Alternatively, the web identifier could be optical,recognizing reflective strips on the slats, or some other sensingsystem.

As previously set forth, web sensor 502 supplies a signal that varies asthe speed of web 12 to linear motor controller 504 moves along with anidentification of one or more index slats. In return, linear motorcontroller 504 supplies digital signals, which are separate inputs toaddressable interface 512 in order to control the respective linearmotor drive 506. A control program 520 run by controller 504, or othercomputer, operates a closed-loop control algorithm in order to maintaina closely regulated speed of web 12. In the illustrative embodiment, web12 is regulated at a nominal speed with a variation of plus or minus 2.5percent or less. A state machine 540 is used to monitor the state of thelinear motor propulsion control system and to ensure that adequatecontrol is made over the speed of the web by assigning errors for eachof different states. Propulsion control system 500 controls the linearmotor controllers 504 in a manner which operates the linear motorprimaries as close to its desired speed without exceeding the attractiveforce on the slats.

As is conventional, and as is understood by those skilled in the art,the output of a variable frequency linear motor drive 506 varies, suchas between 0 hertz and maximum frequency, such as 120 hertz, and obtainsa thrust output with the corresponding linear motor primary 28 whichvaries as a function of the frequency output of the linear motor drive.As is also known in the art, the relationship between this frequency andthe thrust is a somewhat bell curve, such that maximum thrust isproduced at an intermediate value between the maximum and minimum (FIG.19). In the illustrative embodiment, the control program 520 controlsthe output of linear motor drive 506 on one side or the other of themaximum thrust value of the frequency curve. Conventionally, the frontside of the curve F, between 0 hertz and the maximum thrust, is used.However, it is contemplated that the control program may operate on thebackside B of the thrust verses hertz curve, namely for frequency valuesbeyond those at which maximum thrust is obtained and higher frequenciesabove that value. When operating on this back side B of the curve, it ispossible to obtain even higher thrust values FT for lower amounts ofattraction force FA between the linear motor primary 28 and the slats,thereby reducing the tendency of the motors to lift the slats in lowerrun 14 off of the support track network 19.

Control program 520 includes a target speed and compares motion of theslats to compute an error term and uses approximations to generate asignal that runs the linear motor drive. The control loop is a digitalproportional integral derivative (PID) controller, but other closed-loopcontrol techniques may be utilized, such as analog control loops, andthe like. Because of the requirement for ever-smaller gaps, it isdesirable to minimize variation from one conveyor surface to another,such as from an induct, or feed conveyor, to the sortation assembly. Anyspeed variation may increase or compress gaps between articles. Speedvariation may occur, for example, when the conveyor has a full-packagedload and abruptly discharges many packages, then the abrupt changed loadcould lead to speed changes. The present closed-loop propulsion controlsystem avoids problems with conventional open-loop drives for sorterassemblies. The sorter assembly 10 may include an idle mode, wherein, ifpackages are not detected upstream of the sorter assembly, the speed ofthe sorter assembly may be decreased to a reduced speed, such as, forexample, to one-half of the speed, or the like. This may reduce wear andenergy consumption, as well as avoiding the need to increase the speedback up to full-operating speed, when articles are, again, supplied tothe sorter.

It is further determined that design parameters also may be selected ina manner which minimizes attractive force while maximizing forwardthrust. In the illustrative embodiment, for a sortation bed of betweenapproximately 1.2 meters to approximately 1.6 meters wide, it has beendetermined that the following dimensions are useful in producing thedesired thrust FT without exceeding the attractive force FA that wouldsubstantially lift slats in lower run 14 off their support rails:

-   -   Secondary width (laterally of conveying surface): approximately        160 mm to approximately 180 mm.    -   Secondary length (longitudinal of conveying surface):        approximately 110 mm to approximately 120 mm.    -   Thickness: approximately 4 to approximately 6 mm.    -   Magnetic gap (MG): approximately 8 mm to approximately 9 mm.    -   Slat gap (SG): approximately 2 mm to approximately 3 mm.

In the illustrative embodiment, 7.5 to 8.5 amps are supplied to thelinear motor primaries. As an example, motor primary spacing may beapproximately every 8 meters of conveyor length. This would involve, byway of example, 20 to 25 linear primary motors for a 120-meter sorter.However, it should be understood that these design parameters might varydepending upon the load, speed and other parameters of the conveyorsorter assembly.

A cooling system 314 is provided for primaries 28. Cooling system 314includes a heat sink 310 having a series of heat-dissipating fins 311and a fan 312. Fins 311 are oriented generally laterally of conveyingsurface 312. Because primaries 28 are longitudinally elongated, fins 311are elongated in the short dimension of the primaries. This providesreduced temperature gradients on the primaries. Fan 312 may be combinedwith a plenum 313 to direct airflow across fins 311. In this manner, fan312 may be oriented in various directions, or may be multiple fans, andstill direct the air over fins 311.

The linear motor propulsion system may be a non-synchronous type,wherein magnet plate 64 is made from a metallic material that conductsmagnetism. Examples of such magnetically permeable materials includecarbon steel, iron and other such known permeable materials. In theillustrated embodiment, magnet plate is made from cold-rolled steel.Alternatively, the linear motor propulsion system may be a synchronoussystem for which magnet plate 64 would be a permanent magnet, such asferrite, aluminum-nickel-cobalt, or the like. For a synchronous system,the magnet plate would typically be mounted at the slat, but outside ofthe interior such that the aluminum wall of the slat is not part of thesecondary. This could occur by making the magnet plate a part of thewall of the slat or by mounting the magnet plate, or plates, to anexterior surface of the slat. Applications for such synchronouspropulsion systems, which enjoy an increase in motor efficiency overnon-synchronous ones, are applications where the presence of a permanentmagnet would not affect the nature of the articles being sorted or othermetallic objects in the presence of the sorter assembly.

Of course, it may be desirable to create a sorter assembly having acombination synchronous and non-synchronous linear motor system. Forexample, primaries driving the top run of the web from below could beoperated as synchronous linear motors by producing thrust in magneticmagnet plates outside of the slat interior, while primaries driving thebottom run of the web from above could be operated as non-synchronouslinear motors by producing trust in magnetically permeable magnet platesin the slat interior. This would allow the motors driving the upper runto assert more thrust without the need to be concerned about attractionforce, while the motors driving the lower run apply sufficient thrust tokeep the slats in the lower run moving, but without assertingsignificant thrust on the web as a whole. An advantage of the presentinvention operated at least in part as a synchronous linear motorpropulsion system, is that the magnet plate, which is magnetic, would beon the side of the slat opposite the conveying surface. This wouldsignificantly reduce the threat to goods being sorted, from the magneticfield of the magnet plates.

Control of the linear motor primaries in order to avoid lifting theslats in the bottom run may be seen by reference to FIGS. 20 a and 20 b.They illustrate the relationship between linear speed of each motor,slat speed and frequency applied to the linear motor primary. To preventslats from lifting off slat supports in the bottom run, the motor speedminus slat speed (also known as slip) must be sufficiently high.Alternatively, for lower values of slip, the motor current must besufficiently reduced, to avoid exceeding a particular attractive force.In other words, the linear speed of the motor has to be higher than thelinear speed of the slat so that, at least on the bottom run, the linearmotor cannot run close to synchronous speed. However, it may beundesirable to allow the slip to go too low. This may require, forexample, that when decreasing web speed, the power not be decreased tooquickly, or else slat chatter may occur.

In an alternative embodiment illustrated in FIG. 21, a slat 20 cincludes upper and lower magnet plates 64, 64′ which are retained inposition by horizontal extensions 154, 156, 158 and 160. Slat 20 c isuseful with a sorter assembly having linear motor primaries that arepositioned to drive the endless web from both sides of the web, i.e.,from both inside and outside of the web. Also, the front wall 38 andrear wall 40 define respective forward convex surface 33 c and rearconcave surface 33 d that extend approximately equidistant fromrespective channels 44, 46 such that mounting portions 52 and 54 aregenerally equidistant between top and bottom walls 34, 36.

In another embodiment illustrated in FIG. 22, a slat 20 d includes amagnet plate 64 in only an upper portion thereof. The magnet plate wouldbe driven by a linear motor primary positioned outside of the endlessweb, such as from below the sorter assembly. Slat 20 d includes achannel 44 having a generally T shape thereby combining channel 48 withchannel 44. This allows the lateral stabilizer to be incorporated withthe bearing means in a composite channel. In this manner, the lateralstabilizer is also outside of the magnetic interface that is definedbetween magnet plate 64 and the linear motor primary (not shown).

In another alternative embodiment illustrated in FIG. 23, a pusher shoe26″ is shown having a glide portion that is propelled along diverterassembly 16 by a pin 32 and bearing 30 mounted by a support portion 78.Detents 65 and 66 included in respective walls 56, 58 are shownretaining the respective magnet plates 64, 64′ in their respectivereceiving sections 60, 62 of slat 20 d by an interference fit.

In another alternative embodiment illustrated in FIG. 24, a slat 20 eincludes a magnet plate 64 that is mechanically interlocked with theslat by a series of extruded rails 67 extending from a supportingsurface thereof that are deformed as the magnet plate is inserted in theslat. It would be apparent to one of ordinary skill in the art that asimilar arrangement with rails could be utilized to support a linearmotor secondary plate at the bottom portion of the slat as well or aplate only at the bottom portion of the slat.

In yet another alternative embodiment illustrated in FIG. 25, a slat 20f includes a concave rear wall 40 having an upper section 172, a lowersection 174 and a middle section 176. Upper section 172 and lowersection 174 are each formed with a planar surface 178 extending betweenends 179 of the upper and lower surfaces, respectively. However, thesurface defined by sections 172, 174 and 178 is a generally arcuatesurface. Planar surfaces 174, 178 permit the deformation of rear wall40′, such as, for example, by peening, to thereby provide a mechanicalinterlock with the linear motor magnet plates 64, 64′.

With reference to FIGS. 27–34, a frame 148 of sortation conveyor 10includes at least two elongated horizontal members 150 a, 150 b eachdefining fastener channels 151 along the respective horizontal membersfor attachment of items by fasteners 153 at selectable locations alongthe horizontal members. Such items may include diverter assemblies 16,linear motor primaries 28, and the like. Elongated members 150 a, 150 bmay be extruded metal. Other items that may be attached to frame members150 a, 150 b by fasteners include a plurality of vertically extendinglegs 152. Each leg 152 is formed having an attachment plate 154positioned along interior surface 155 and proximate to top 156. Eachattachment plate 154 has a plurality of through-holes 158. Each leg 152is vertically adjustable by, for example, a base 157 formed with aplurality of vertically oriented and slightly slanted slots 157′, whichare placed in selective registration with through-holes 157″ of leg 152.

Fasteners are used to secure base 157 to leg 152. Fastener channels 151define a track assembly defined by an upper track 160 and a lower track164 positioned a pre-selected distance apart. Fastener channels may alsobe present on exterior surface 161 of upper track 160 as provided with aplurality of longitudinal channels 162, while, similarly, exteriorsurface 165 of lower track 164 is provided with longitudinal channels167. Positioned against exterior surface 161 and 166 of upper tracks 160and lower tracks 164, respectively, are side plates 168. Side plates 168include a plurality of upper through-holes 170, a plurality of middlethrough-holes 172, and a plurality of lower through-holes 174.Appropriate fasteners 153, such as, for example, bolts, are positionedthrough upper through-holes 170 of side plates 168 and are securedwithin a channel 162 of upper track 160. Analogously, appropriatefasteners are positioned through lower through-holes 174, and extendwithin channels 166 of lower track 164. Thus, side plates 170, whensecured to the track assembly, maintain the proper distance betweenupper tracks 160 and lower tracks 164. Appropriate fasteners are alsoplaced through attachment plates 154 of legs 152 and secured throughmiddle through-holes 172 of side plates 168 to thereby secure legs 152to upper track 160 and lower track 164.

To provide frame 150 with proper stability, one or more cross supports,or cross braces, 180 extend generally orthogonally between upper tracks160 and lower tracks 164. Cross supports 180 are attached to tracks 160and 164 by side plates 182 attached to ends of 181 of cross supports180. As with side plates 168, side plates 182 are formed with upperthrough-holes 184, middle through-holes 186, and lower through-holes188. Upper through-holes 184 are attached to upper tracks 160 alonginterior surface 163 by inserting fasteners through through-holes 184and securing them within channels 162′. To secure cross supports 180 tolower tracks 164, fasteners are threaded through lower through-holes 188and inserted within channels 166′ formed along interior surface 167. Legsupports 190 are positioned between each pair of legs 152 and attachedto legs 152 by the use of appropriate fasteners. Leg supports 190 aregenerally parallel to cross supports 180 and are positioned belowsupport angles 176.

Linear motor primary supports 192 are attached to adjacent crosssupports 180, and are generally orthogonal thereto. Linear motor primarysupports 192 provide a support surface for the placement of linear motorprimaries 28. One or more diverter assemblies are positioned betweenupper tracks 160 and lower tracks 164 by the use of appropriatefasteners inserted within the inner surfaces of upper and lower tracks160, 164. Alternatively, diverting track assembly 165 may be attached toone or more cross supports 180.

As shown in FIGS. 28 and 29, end 10′ of sortation conveyor 10 is fittedwith a stationary end track assembly 200. Stationary end track assembly200 includes a cross member 202 having a pair of ends 204, which areattached to mounting plates 206. Attached to mounting plates 206 are endtracks 208. Each mounting plate 206 is generally hexagonal in shape andincludes a first section 210 formed with upper through-holes 212, middlethrough-holes 214, and lower through-holes 216. Second section 218 ofmounting plates 206 is generally tapered in shape and includes aplurality of through-holes 220. Each end track 208 has an arcuate ledge222, which serves as a riding surface for first wheels 112 of endmembers 24, and a center section 224 formed with a plurality ofthrough-holes 226. To increase the stability of end tracks 208, aplurality of ribs 227 are provided between interior surface 223 ofarcuate ledge 222, and center section 224.

To assemble stationary end track assembly 200, a plurality of L-shapedbrackets 230 are secured to ends 204 of cross member 202 by the use ofappropriate fasteners. L-shaped brackets 230 have a plurality ofthrough-holes 231 placed in substantial registry with middlethrough-holes 214 of first section 210 of mounting plates 206 andchannels 232 of cross member 202 through which fasteners are placed.Thereafter, end tracks 208 are positioned such that through-holes 226are in registry with through-holes 220 of second section 218 of mountingplates 206 and appropriate fasteners placed there through. Oncestationary end track assembly 200 is assembled, it is positioned betweenupper tracks 160 and lower tracks 164. Appropriate fasteners are thenused to attach upper through-holes 212 and mounting plates 206 tointerior surface 163 of upper track 160 and lower through-holes 216 tointerior surface 165 of lower tracks 164. When in position on sortationconveyor 10, edges 209 of end tracks 208 are substantially aligned withupper edge 160′ of upper track 160 and lower edge 164′ of lower track164 and thereby provides a smooth, continuous interface for movement offirst wheels 112 of end members 24–24″, as slats 20 are conveyed betweenthe return run and upper run of sortation conveyor 10.

Turning now to FIGS. 30–32, opposite end 10″ of frame 148 includesmoveable member 23 and force-producing device 27 which define anadjustable take-up assembly 230. Take-up assembly 230 provides asubstantially constant force upon slats 20 to thereby maintain the samein the proper state of tension, and takes up any slack existing betweenslats 20. Take-up assembly 230 is comprised of two identical sets ofcomponents, each of which is attached to a side 150′ and 150″ of frame150. Therefore, the subsequent description will detail only one set ofcomponents, with the understanding that the identical components areplaced on the opposing side of sortation conveyor 10 along end 10″.

Take-up assembly 230 includes a guide member 232 having a pair ofhorizontally movable slide members 234. Guide member 234 is secured to across member 236 which is attached at its ends to lower tracks 164. Acarriage 238 is attached to upper surfaces 235 of slide members 234 byusing appropriate fasteners placed through through-holes 239. Carriage238 includes an attachment bracket 240, and a cable bracket 242, both ofwhich are attached to, and extend from, side 241 of carriage 238. An endtrack 244 includes an arcuate edge 245, a center section 246, a first orupper flange 247 extending from the upper region of center section 246and a second or lower flange 248 extending from the lower region ofcenter section 246. Upper flange 247 is generally planar while lowerflange 248 is generally L-shaped with a horizontal section 248′preferably integrally attached to arcuate edge 245. Attachment bracket240 of carriage 238 is secured to end track 244 by the use of fastenersplaced through through-holes 240′ of attachment bracket 240 andthrough-holes 244′ of end track 214.

An expansion joint assembly 25 is provided to enable end track 244 tomove in a horizontal direction either towards or away from upper track160 and lower track 164 while maintaining continuity of the track. Jointassembly 25 includes a finger joint 254 and a mounting plate 256. Asshown in FIG. 32, first finger joint 252 includes a mounting section 258having a plurality of through-holes 259 which are placed in registrationwith through-holes 260 formed in end track 244, and secured thereto byappropriate fasteners. When in position, first finger joint 252 ispositioned on interior surface 244′ of end track 244 with upper flange247 being substantially co-planar with fingers 261 of first finger joint252. Second finger joint 254 has a plurality of fingers 262 and amounting section 264. Upper track 160 is formed with a cutout section266 into which second finger joint 254 is positioned. Once in position,second finger joint 254 is aligned with upper track 160 such thatfingers 262 are generally co-planar with top edge 160′ of upper track160, while mounting section 264 is positioned beyond external surface161 of upper track 160 and secured thereto by fasteners extendingthrough through-holes 264′. Mounting plate 256 is positioned along innersurface 163 of upper track 160 and beyond surface 255 of second fingerjoint 254. A cross member 268 extends orthogonally between upper trackassemblies 160, with each end including two top attachment brackets 270and two side attachment brackets 272. Top attachment brackets 270 eachhave a horizontal section 270′ and a vertical section 270″, both ofwhich are equipped with a through-hole 271. Side attachment brackets 272are also equipped with a pair of through-holes 273. Side attachmentbrackets 272 attach cross member 168 to upper track assembly 160 by theinsertion of appropriate fasteners through through-holes 273 andchannels 269 of cross member 268, and channels 162′ of upper track 160.Vertical section 270″ of top attachment brackets 170 is placed inregistration with mounting plate 256. Specifically, mounting plate 256is positioned so that through-hole 256′ is placed in registry with athrough-hole 264′ of mounting section 264 of second finger joint 254 toallow passage of a fastener there through, while the other topattachment bracket 270 is placed in registration with through-hole 256″of mounting plate 256. An appropriate fastener is placed there throughand extends within channel 162′ formed in interior surface 163 of uppertrack 160.

To provide the necessary force upon end tracks 244 of take-up assembly230, force-producing device 27 in the form of an adjustable forceassembly 275 is provided which imparts a constant force upon end tracks244 to thereby maintain the same in the proper position and thereby takeup slack within slats 20. Adjustable force assembly 275 may include anadjustable weight system 277, and a pulley system 279. Pulley system 279includes a first pulley 281 attached to a first pulley support 283, anda second pulley 285 attached to a second pulley support 287. Firstpulley support 283 is attached to exterior surface 165 of lower trackassembly 164 and includes a plurality of through-holes 284 through whichfasteners are inserted therein to secure the same to lower track 164.Similarly, second pulley support 285 includes through-holes 286,enabling the same to be attached to middle through-holes 172 of sideplate 168.

Weight assembly 277 includes a pair of spaced, vertically orientedL-shaped alignment members 289 which may be adjustable by adding orsubtracting weight. Alignment members 289 are spaced from the exteriorsurface 165 of lower track 164 by spacers 290, and attached therethrough by appropriate fasteners placed through through-holes 291.Positioned between alignment members 289 are a plurality of removableweights 292, each of which includes a keyhole-shaped slot 293dimensioned to receive a weight-retaining member 294.

A drive member, such as, for example, a cable 296, is attached toweight-retaining member 294 and trained about first pulley 281 andsecond pulley 285. Cable 296 is attached at its opposing end to cablebracket 242 of carriage 238, which extends between upper track 160 andlower track 164. A generally L-shaped upper support member 298 isattached to upper track 160 and projects there above. Attachment ofupper support member 298 is achieved by the placement of fastenersthrough through-holes 299 and secured within upper track 160. Uppersupport member 298 is formed with a cutout section 300 dimensioned topermit mounting section 264 of second finger joint 254 to be attached toupper track 160.

Frame end 200 has a shape that is substantially circular, namely, aportion of a circle. Alternative frame ends 200′ and 200″ have shapesthat are non-circular. Frame end 200′ has a non-circular shape that issymmetrical about a horizontal axis H. An example is a parabola. Frameend 200″ has a non-circular shape that is not symmetrical about ahorizontal axis H. The shape has a lower curvature at an upper portionand a higher curvature at a lower portion, although the lower curvaturecould be at the bottom portion and the higher curvature at the lowerportion. The purpose of such non-circular curve is to reduce noise bycontrolling acceleration of the web at one or both transition portions.Such a non-circular shaped frame end at one end of the frame could becombined with a circular-shaped frame end at the opposite end of theframe or another non-circular shaped frame end at the opposite end ofthe frame.

As can be seen, the present invention provides a positive displacementsortation system and method that has many advantages over prior systems.Moreover, the various aspects of the invention may be utilizedseparately or in combination. For example, the unique shoe and slatconfiguration may be utilized with a conventional rotary motor and chaindrive or may be utilized with other linear motor propulsion systems,such as the type disclosed in commonly assigned U.S. Pat. No. 5,588,520,the disclosure of which is hereby incorporated herein by reference.Likewise, the unique linear motor propulsion system disclosed herein maybe utilized with other sorter configurations including other positivedisplacement shoe and slat sorters as well as other sorterconfigurations, such as tilt-tray sorters, cross-belt sorters, and thelike. The various unique aspects of the frame may be used individuallyand with other types of positive displacement shoe and slat sorters.

Changes and modifications in the specifically described embodiments canbe carried out without departing from the principles of the inventionwhich is intended to be limited only by the scope of the appendedclaims, as interpreted according to the principles of patent lawincluding the doctrine of equivalents.

1. A positive displacement sorter apparatus for sorting articles to aplurality of spurs, comprising: a plurality of interconnected slatsdefining an endless web having upper and lower runs, said upper run ofsaid web defining a conveying surface; a plurality of pusher shoes, eachtraveling along at least one of said slats to laterally displacearticles on said conveying surface; a plurality of diverter assemblies,each of said diverter assemblies for laterally propelling a plurality ofsaid pusher shoes laterally of said conveying surface toward one of thespurs in order to divert an article to that spur, each of said diverterassemblies comprising at least two generally parallel guide railsextending diagonally under said upper run of said web and at least twoactuators, each for actuating pusher shoes toward the one of said guiderails associated with that actuator; a linear motor propulsion systemfor propelling said endless web, said linear motor propulsion systemcomprising a plurality of primaries and a plurality of secondaries, saidplurality of secondaries joined with said slats; a control, said controlcontrolling said linear motor propulsion system for propelling saidendless web at a controlled speed, said control controlling saiddiverter assemblies for diverting articles to selected spurs, saidcontrol operating at least one of said actuators to cause said at leastone of said actuators to actuate at least one of said pusher shoestoward the associated one of said guide rails to divert an article tothe associated spur.
 2. The sorter apparatus of claim 1 wherein each ofsaid slats has an upper surface portion that is generally planar.
 3. Thesorter apparatus of claim 1 wherein said actuators compriseelectromagnetic actuators that magnetically attract the pusher shoes. 4.The sorter apparatus of claim 3 wherein each of said pusher shoesincludes an elongated transfer assembly below said conveying surface forengaging one of said guide rails, said actuators magnetically attractingsaid transfer assembly.
 5. The sorter apparatus of claim 3 wherein eachof said pusher shoes includes a bearing below said conveying surface forengaging one of said guide rails, said actuator magnetically attractingsaid bearing.
 6. The sorter apparatus of claim 1 wherein said controloperates a state machine for controlling said linear motor propulsionsystem, said state machine operating in one of a plurality of states. 7.The sorter apparatus of claim 6 wherein said plurality of statescomprise at least an acceleration state during which said linear motorpropulsion system is accelerating said web, an idling state during whichno adjustment is being made to the speed of said web, and a decelerationstate during which said linear motor propulsion system is deceleratingsaid web.
 8. The sorter apparatus of claim 1 wherein each of saiddiverter assemblies comprising at least three generally parallel guiderails extending diagonally under said upper run of said web and at leastthree actuators, each for actuating pusher shoes toward the one of saidguide rails associated with that actuator.
 9. A positive displacementsorter apparatus for sorting articles to a plurality of spurs,comprising: a plurality of interconnected slats defining an endless webhaving upper and lower runs, said upper run of said web defining aconveying surface; a plurality of pusher shoes, each traveling along atleast one of said slats to laterally displace articles on said conveyingsurface; a plurality of diverter assemblies, each of said diverterassemblies for laterally propelling a plurality of said pusher shoeslaterally of said conveying surface toward one of the spurs in order todivert an article to that spur, each of said diverter assembliescomprising at least two generally parallel guide rails extendingdiagonally under said upper run of said web and at least two actuators,each for actuating pusher shoes toward the one of said guide railsassociated with that actuator; a linear motor propulsion system forpropelling said endless web, said linear motor propulsion systemcomprising a plurality of primaries and a plurality of secondaries, saidplurality of secondaries joined with said slats; a control, said controlcontrolling said linear motor propulsion system for propelling saidendless web at a controlled speed, said control controlling saiddiverter assemblies for diverting articles to selected spurs, saidcontrol measuring lengths of articles, said control operating said atleast two actuators to cause each of said at least two actuators toactuate one of said pusher shoes toward the associated one of said guiderails to divert an article having a length below a particular length,said control operating no more than one of said at least two actuatorsto actuate a plurality of said pusher shoes toward the associated one ofsaid guide rails to divert an article having a length greater than saidparticular length.
 10. The sorter apparatus of claim 9 wherein each ofsaid slats has an upper surface portion that is generally planar. 11.The sorter apparatus of claim 9 wherein said actuators compriseelectromagnetic actuators that magnetically attract the pusher shoes.12. The sorter apparatus of claim 11 wherein each of said pusher shoesincludes an elongated transfer assembly below said conveying surface forengaging one of said guide rails, said actuators magnetically attractingsaid transfer assembly.
 13. The sorter apparatus of claim 11 whereineach of said pusher shoes includes a bearing below said conveyingsurface for engaging one of said guide rails, said actuator magneticallyattracting said bearing.
 14. The sorter apparatus of claim 9 whereinsaid control operates a state machine for controlling said linear motorpropulsion system, said state machine operating in one of a plurality ofstates.
 15. The sorter apparatus of claim 14 wherein said plurality ofstates comprise at least an acceleration state during which said linearmotor propulsion system is accelerating said web, an idling state duringwhich no adjustment is being made to the speed of said web, and adeceleration state during which said linear motor propulsion system isdecelerating said web.
 16. The sorter apparatus of claim 9 wherein eachof said diverter assemblies comprising at least three generally parallelguide rails extending diagonally under said upper run of said web and atleast three actuators, each for actuating pusher shoes toward the one ofsaid guide rails associated with that actuator.
 17. A positivedisplacement sorter apparatus for sorting articles to a plurality ofspurs, comprising: a plurality of interconnected slats defining anendless web having upper and lower runs, said upper run of said webdefining a conveying surface; a plurality of pusher shoes, eachtraveling along at least one of said slats to laterally displacearticles on said conveying surface; a plurality of diverter assemblies,each of said diverter assemblies for laterally propelling a plurality ofsaid pusher shoes laterally of said conveying surface toward one of thespurs in order to divert an article to that spur, each of said diverterassemblies comprising at least two generally parallel guide railsextending diagonally under said upper run of said web and at least twoactuators, each for actuating pusher shoes toward the one of said guiderails associated with that actuator; a linear motor propulsion systemfor propelling said endless web, said linear motor propulsion systemcomprising a plurality of primaries and a plurality of secondaries, saidplurality of secondaries joined with said slats; a control, said controlcontrolling said linear motor propulsion system for propelling saidendless web at a controlled speed, said control controlling saiddiverter assemblies for diverting articles to selected spurs, saidcontrol operating at least one of said actuators to cause said at leastone of said actuators to actuate at least one of said pusher shoestoward the associated one of said guide rails to divert an article tothe associated spur; and each of said pusher shoes comprising a bodymolded from a plastic material and a plurality of lubricating strips,each of said lubricating strips at an interface between that pusher shoeand the associated one of said slats, wherein said plastic materialcomprises a durable plastic material.
 18. The sorter apparatus of claim17 wherein each of said slats has an upper surface portion that isgenerally planar.
 19. The sorter apparatus of claim 17 wherein saidactuators comprise electromagnetic actuators that magnetically attractthe pusher shoes.
 20. The sorter apparatus of claim 19 wherein each ofsaid pusher shoes includes an elongated transfer assembly below saidconveying surface for engaging one of said guide rails, said actuatorsmagnetically attracting said transfer assembly.
 21. The sorter apparatusof claim 19 wherein each of said pusher shoes includes a bearing belowsaid conveying surface for engaging one of said guide rails, saidactuator magnetically attracting said bearing.
 22. The sorter apparatusof claim 17 wherein said control operates a state machine forcontrolling said linear motor propulsion system, said state machineoperating in one of a plurality of states.
 23. The sorter apparatus ofclaim 22 wherein said plurality of states comprise at least anacceleration state during which said linear motor propulsion system isaccelerating said web, an idling state during which no adjustment isbeing made to the speed of said web, and a deceleration state duringwhich said linear motor propulsion system is decelerating said web. 24.The sorter apparatus of claim 17 wherein each of said diverterassemblies comprising at least three generally parallel guide railsextending diagonally under said upper run of said web and at least threeactuators, each for actuating pusher shoes toward the one of said guiderails associated with that actuator.